These detection devices typically comprise a casing, defining a chamber having an inlet for a fluid to be subjected to pressure measurement, a pressure sensor accommodated in the casing and a circuit arrangement, to which the pressure sensor is electrically connected; the circuit arrangement typically includes a printed circuit board at least partially accommodated in the chamber of the casing.
Two types of sensors, referred to herein as “monolithic sensors” and “semiconductor sensors” for the sake of simplification, are mainly used for the production of the indicated detection devices. The characteristic that immediately distinguishes the two types of sensors are the dimensions, the semiconductor sensors being definitely smaller with respect to monolithic sensors.
A typical monolithic sensor is schematically represented in FIGS. 1 and 2, where it is indicated in its entirety with 1. Such sensor typically comprises a monolithic body 2, generally cylindrical shaped and usually made of ceramic material (as a matter of fact, sensors of the type in question are also referred to as “ceramic sensors”). The monolithic body 2 has a blind cavity 3, having a substantially circular section, closed at an end by a membrane portion 4 of the monolithic body 2. An electrical detection component, capable of generating a signal representing a flexure of the membrane portion 4, is provided for at the membrane portion 4; the components used for such purpose are typically selected from among resistor elements, capacitive elements and piezo-resistive elements. The detection component (or a group of such elements) is mounted on a printed circuit board, indicated with 5 in FIG. 1, provided with terminals or pins 5a, which is fixed on the face of the monolithic body 2 opposite to the opening of the cavity 3, in such a manner that the detection element adheres to the surface of the membrane portion 4 outside the cavity 3, so as to be able to detect any flexures thereof.
The sensor 1 is mounted inside the chamber of the detection device in such a manner that the open end of the blind cavity 3 is directly in communication with the inlet conduit of the detection device: for this purpose, the inlet conduit usually has a tubular end part, on which the sensor body 2 is coupled at the open part of the cavity 3. The sensor 1 is connected, through the pins 5a of the circuit 5, to another printed circuit board, present inside the casing, the other circuit in turn being connected to an electric connector of the device; alternatively, the pins 5a may be directly connected to the electric terminals of an electric connector of the device.
When using the sensor device the pressure of the fluid present in the inlet conduit is such to cause a flexure of the membrane portion 4 of the sensor and the degree of such flexure, which depends on the pressure of the fluid, is measured through the detection element belonging to the circuit 5. Through the pins 5a, the output signal of the detection element, representing the pressure value and possibly amplified and/or conditioned by means of suitable components of the circuit 5, reaches the abovementioned other printed circuit board and/or the abovementioned electric connector, through which the sensor device is connected to an external system, such as for example an automobile engine control unit.
The main advantages of the monolithic sensors include easy fixing, capacity to resist against fluids aggressive from a chemical point of view and the optimal general mechanical resistance, which facilitates manipulation and mounting the component during the production of the pressure detector device.
Regarding the semiconductor pressure sensors instead, they are substantially configured as integrated circuits or chips and thus they are definitely smaller with respect to a monolithic sensor, though they also have a deformable detection membrane.
The sensor body is in this case made up of a so-called “die”, i.e. a small block or plate made of semiconductor material, typically silicon, which defines a detection membrane. Also the die of a semiconductor pressure sensor may be made in such a manner to define a small cavity closed at an end by a respective membrane portion, or the die may form the membrane alone and be fixed, for example glued, on a respective substrate, typically made of glass, defining an axial cavity.
Directly obtained on the die made of semiconductor material is the miniaturised electric circuit of an integrated circuit serving to detect the degree of deformation of the detection membrane. The die may also be enclosed in a respective casing or container, referred to as “package”, projecting from which are the connection terminals (pins), conceived to connect the die itself to a circuit support, of the printed circuit board intended to be mounted inside the respective pressure sensor device.
As an example, FIG. 3 schematically illustrates a printed circuit board 6 provided for use in a pressure detector device. The circuit 6 comprises circuit support, or PCB (Printed Circuit Board) or terminal board 7, for example made of glass fibre, provided with electrically conductive tracks 7a at the surface, connected to which are the electrical connections or pins (not shown) of a semiconductor pressure sensor, indicated in its entirety with 8, showing only the package. Devices of this type are described, for example in U.S. Pat. Nos. 6,272,913 B1 and 6,212,946 B1.
The semiconductor pressure sensors allow directly obtaining or integrating the detection circuit components on the die, comprising those for possibly amplifying and/or conditioning the signal, allowing reducing production costs. However, due to the miniaturised dimensions and the inherent fragility of this type of components, the semiconductor sensors complicate, from an industrial point of view, the production of pressure sensor devices to an extent. For example, the semiconductor pressure sensors should be mounted on a printed circuit board support of the pressure sensor device, with such circuit support required to be positioned in such a manner to face or to be extended at least partially inside a detection chamber defined in the casing of the device itself, whose chamber is in communication with the inlet conduit of the fluid. This need complicates the production of the pressure sensor device. Furthermore, especially in case of devices provided for detecting the pressure of liquids, particular expedients for sealed insulation of the part of the circuit that supports the pressure sensor must be provided for (for such purpose see the abovementioned U.S. Pat. Nos. 6,272,913 B1 and 6,212,946 B1).